SEMIPERMEABLE COMPOSITE MEMBRANE

A semipermeable composite membrane on a microporous substrate, such as a polysulphone membrane having on its surface a semipermeable membrane being the reaction product of a polyamine, a water soluble polymer of formula 1 (1) wherein R is hydrogen or an hydrocarbongroup, x is 50 - 99.9%, and y is 100-x mol.% and n indicates the molecular weight and of a crosslinking agent containing a polyfunctional group having reacted with the amino groups of the polyamine and of the polymer. In the formula 1 preferably R is an alkylgroup of 1-5 carbon atoms, particularly methyl,and n is equivalent to a value providing a mol.weight of the polymer of more than 10,000. The water soluble polymer is advantageously a mixture of a polymer of formula 1 wherein x and y are both 50 mol.% and a polymer of formula 2, (2) this last mentioned polymer being preferably obtained by hydrolysis of a compound of formula 1. The degree of hydrolysis is preferably 70 to 99.9%. The crosslinking agent is preferably a mixture of isophthaloylchloride and trimesoylchloride; the polyamine is preferably an azaalkane compound having terminal amino groups with a straight chain comprising 8 to 24 carbon atoms, particularly 1,10-diamino-4,7-diazadecane; 1,14-diamino-4,8,11-triazatetradecane and 1,18-diamino-4,8,11,15-tetraazaocta-decane. The flux of the membrane is at least 40 1/m2.h and the salt retention at least 90%.